Recent advances in resist patterning methods have been introduced using physical, three dimensional, pattering members to imprint a pattern in a thin film useful as a mask for the etching of an underlying layer over which the patterned mask layer is formed. Pursuant to this pattern forming method, a plate known as template is used. On the surface of the template (patterned surface), an embossed three dimensional pattern, corresponding to a negative of the three dimensional pattern to be formed on the substrate or film layer (resist), and an alignment mark for aligning the template to a substrate or film layer on which the three dimensional pattern is to be transferred, are formed. The negative three dimensional pattern on the template, when applied to a thin film, results in an opposite, positive three dimensional pattern having protrusions and recesses opposite or negative in nature to the protrusions and recesses on the template, being formed on the thin film. This patterned thin film may be used as a masking layer for etching an underlying film, wherein the mask and the portions of the layer underlying the mask which underlie the recesses is exposed to an etchant, and in the recess areas of the resulting masking layer the underlying film layer or substrate is exposed to the etchant, and thus etched, but where the protrusions in the mask layer protect the underlying material from exposure to the etchant, etching of the underlying material is substantially prevented. As a result, a pattern corresponding to the pattern in the mask layer is etched into, and thus transferred to, the underlying material.
The above described template is useful for forming patterns in photocurable resins, including photoresist, resist layers including layers used as masking layers in the fabrication of semiconductor and other devices. Where the resist material used for the fabrication of a mask is a photoresist, that is, a resist which is activated by exposure to light, this optical imprint method is often carried out in the following steps or sequence of operations:
1. an operation in which a photocuring resin is coated on the surface of the substrate for processing;
2. an operation in which the surface of the substrate for processing and the pattern surface of the template are aligned with one other;
3. an operation in which the pattern surface of the template is brought into, and maintained in contact with, the photocuring resin for a prescribed time, such that the photocuring resin fills the recessed portions of the pattern surface due to the capillary phenomenon;
4. an operation in which the photocuring resin is cured by irradiation by light; and
5. an operation (mold releasing) in which the template is removed from the cured photocuring resin (resin pattern), such that the remaining resin pattern is useful as a mask to etch a pattern corresponding to the mask in the underlying material of or on the substrate.
Repeated use of the mask to form a pattern for an etch mask has been hampered by the occurrence, after releasing of the template from the photoresist material, of the photocuring resin sticking on the emboss pattern of the template. Consequently, it is necessary to clean the template of this adhered photoresist material intermediate of the processing of one or more substrates therewith. The methods of cleaning the template commonly include a dry process using plasma and/or a wet process using a chemical solution.
When the template is cleaned, in addition to the emboss pattern, the alignment mark is also exposed to the plasma or chemical solution. As a consequence, the alignment mark is degraded during the cleaning of the template.